Reaction-based two novel fluorescent probes for Hg2+ detection using benzothiazole derivatives via ESIPT mechanism in aqueous solution and serum

Fast tracking of Hg2+ ions in living cells, food, and environmental samples using a new mitochondria-targeted red emitting probe and its portable applications

Mercury is one of the most hazardous heavy metals and is capable of biomagnification, thereby posing severe risks to ecosystems and human health. Therefore, selective, sensitive, and rapid detection of Hg2+ in a wide range of samples is essential. Herein, we report the synthesis of a new 2-(benzo[d]thiazol-2-yl) phenol-based fluorescent probe (PyS) and its potential as a fluorescent probe for detecting Hg2+ ions in various real samples such as rice, garlic, shrimp, and root samples. When interacting with Hg2⁺, the non-fluorescent probe solution emitted strong red fluorescence at 638 nm in a solution of DMSO/H2O (1/9, v/v). The other ions showed no significant interference during Hg2+ detection. In addition, PyS displayed a rapid response time among the reaction-based systems (3-4 min), low detection limit (72.5 nM), linear response trend in the range of 0-22.00 μM, and large Stokes shift (243 nm). Additionally, PyS can serve as a paper, cotton swab, and polysulfone capsule kit for qualitative detection of Hg2⁺, enabling on-site quantitative detection of Hg2⁺ in beach soil and water samples using a smartphone app. It also can effectively detect Hg2⁺ in living cells in a concentration-dependent manner, thereby highlighting its potential for bioimaging in living organisms.

Review on Synthesis of 2-(2-Hydroxyaryl) Benzothiazoles (HBT) for Excited-State Intra-molecular Proton Transfer (ESIPT)-Based Detection of Ions and Biomolecules

In this review, we present a systematic and comprehensive summary of the recent developments in the synthetic strategies of 2-(2-hydroxyarylsubstituted)-benzothiazole (HBT) framework along with incorporation of various substituents on phenolic and benzothiazole rings which affect the emission process. The literature, spanning the years 2015-2024, on excited-state intramolecular proton transfer (ESIPT)-based studies of HBT derivatives comprising the effects of solvent polarity, substituents, and extended conjugation on fluorophores has been searched. ESIPT, intramolecular charge transfer, and aggregation-induced emissions enable these fluorescent probes to specifically interact with analytes, thereby altering their luminescence characteristics to achieve analyte detection. These fluorescent probes exhibit large Stokes shifts, high quantum yields, and excellent color transitions. Finally, the applications of HBTs as ESIPT-based fluorescent probes for the detection of cations, anions, and biomolecules have been summarized. We anticipate that this review will provide a comprehensive overview of the current state of research in this field and encourage researchers to develop novel ESIPT-based fluorophores with new applications.

ESIPT-based probes for cations, anions and neutral species: recent progress, multidisciplinary applications and future perspectives

Fluorescent and colourimetric probes for small analytes (cations, anions and neutral molecules) have drawn significant attention in recent years. These probes interact with analytes and induce spectral change due to the variations in the photo-physical properties of the fluorophore/chromophore used. Among several photo-physical mechanisms, ESIPT (excited state intramolecular proton transfer) based probes are more advantageous due to their photo-physical properties viz. solvent polarity effect, large spectral shift with multi-channel fluorescence, high quantum yield etc. In recent years, ESIPT-based probes have shown several promising applications, especially monitoring small analytes in biological samples, smartphone app-assisted heavy metal detection in environmental samples, inkless writing, anti-counterfeiting applications etc. Therefore, this review is dedicated to recently reported ESIPT-based probes for small analytes. We have highlighted the organic units responsible for the ESIPT mechanism, their photo-physical parameters, selectivity and sensitivity properties and recent advances in their applications.

Bio-mimetic selectivity in Hg2+ sensing developed via electro-copolymerized PEDOT and benzothiazole-Au nanoparticles composite

To eliminate the potential health risks of mercury, development of stable and selective mercury sensor with high sensitivity is the need of the hour. To address this, a novel PEDOT-AA-BTZ-Au-based Hg2+ selective, hybrid electrochemical sensor has been designed by following a simple protocol for electrode fabrication. The electrode was designed by carefully optimizing the onset oxidation potential of supramolecule 2-(anthracen-9-yl)benzo[d]thiazole (AA-BTZ) and conducting polymer poly-(3,4-ethylenedioxythiophene) (PEDOT), using copolymerization approach followed by dropcasting of gold nanoparticles (AuNPs). The designed electrode offered synergistic effects thus augmenting the electrical conductivity and adsorption capacity as depicted by its porous surface morphology. The highly sensitive analytical signal was generated by sulphur pockets present in AA-BTZ and PEDOT conducting framework. This is further complemented by the selectivity offered by the soft interactions between AuNPs and Hg2+ resulting in a low detection limit of 0.60 nM. The prepared system was further utilized for sensing Hg2+ ion in real systems including lake water and cosmetic samples. Low interference from other ions and better reproducibility further established the suitability of the designed transducer system for future on-site sensing.

A novel dual-function probe for fluorescent turn-on recognition and differentiation of Al3+ and Ga3+ and its application

In this study, a novel dual-function probe BMP based on benzothiazole was easily synthesized and characterized through common optical technique. In the system consisting of DMF/H₂O (v/v, 2/3), probe BMP showed azure and blue-green to Al³⁺ and Ga³⁺, respectively. Besides, the binding ratios of BMP to Al³⁺ and Ga³⁺ were determined as 1:1, which confirmed by Job's plot. Furthermore, for Al³⁺ and Ga³⁺, the limit of detection (LOD) was determined to be 1.51 × 10^-6 M and 4.28 × 10^-6 M, respectively. Moreover, it was worth noting that BMP showed good performances in paper colorimetry, cell phone colorimetric identification and cell imaging.

Lipid droplet polarity decreases during the pathology of muscle injury as revealed by a polarity sensitive sensor

Revealing the relationship between lipid droplets (LDs)polarity and disease is indispensable in clinicopathological diagnosis. So far, muscle injury is often ignored as it is not life-threatening as cardiovascular and cerebrovascular diseases, making the exploration of the internal relationship between muscle injury and LDs polarity a gray area. Herein, a fluorescent probe (CCB) with powerful polar-sensitive as well as precise LDs targeting was designed for visualizing the LDs polarity in the pathology of muscle injury. By means of the probe CCB, the identification of cancer cells and the monitoring of LDs polarity changes in dysfunctional cells were successfully realized. Furthermore, the penetration ability of CCB in tissues of mice was tested to verify the applicability of the probe in organisms. Importantly, by CCB, the relationship between muscle damage and LDs polarity was explored, revealing that muscle damage caused a significant decrease in LDs polarity accompanied by a significant increase in fluorescence. Most importantly, it is the first time to reveal the relationship between muscle damage and LDs polarity. Therefore, the probe CCB will be a powerful monitoring platform for diagnosing related diseases caused by abnormal LDs polarity.

Synthesis of bifunctional fluorescent nanohybrids of carbon dots-copper nanoclusters via a facile method for Fe3+ and Tb3+ ratiometric detection

In this work, a dual-emission ratiometric fluorescent probe of carbon dots-copper nanoclusters (CDs-Cu NCs) nanohybrids with bifunctional features was successfully assembled through mechanical mixing. The CDs were synthesized using ascorbic acid as a carbon source, and Cu NCs were prepared using d-penicillamine as the stabilizer and reducing agent. The as-prepared CDs-Cu NCs displayed two emission peaks (blue at 424 nm and red at 624 nm) when excited at 360 nm, and showed great stability. Interestingly, trace amount of Fe³⁺ could lead to the aggregation of Cu NCs, and induce a drastic static fluorescence quenching at 624 nm because of the electrostatic combination between them, while the fluorescence of the emission peak at 424 nm remained constant. Moreover, an attractive fluorescence enhancement phenomenon at 424 nm was observed when trace Tb³⁺ was added to the above system, which may due to the combination of fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) mechanisms. Thus, CDs-Cu NCs were applied for the ratiometric detection of Fe³⁺ and Tb³⁺ in aqueous solution, and the detection limit (3σ/slope) was 45 nM and 62 nM with the linear range from 0.01 to 40 μM and 0.1 to 50 μM, respectively. Furthermore, the developed sensor was successfully applied for the detection of Fe³⁺ and Tb³⁺ in real-water samples.